Apparatus for reducing nitrogen oxide contained in exhaust gas

ABSTRACT

An apparatus for reducing NO x  contained in exhaust gas as an exemplary embodiment of the present invention may include: a DOC device primarily oxidizing an exhaust materials containing THC and CO in the exhaust gas by using a first DOC; a CPF device mounted downstream of the DOC device to receive the exhaust gas primarily oxidized by the DOC device, further oxidizing the exhaust materials containing the THC and the CO by heat generated during the primary oxidation and an oxidizing agent coated therein, and oxidizing NO in the exhaust gas into NO 2  by using the generated heat and the oxidizing agent coated therein; a nozzle mounted downstream of the CPF device, and dosing a reductant to the exhaust gas; and a SCR device mounted downstream of the nozzle, and reducing NO x  in the exhaust gas into N 2  by using the NO 2  generated in the CPF device and the reductant.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 10-2007-0131563 filed in the Korean Intellectual Property Office on Dec. 14, 2007, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to an exhaust apparatus of vehicles. More particularly, the present invention relates to an apparatus for reducing nitrogen oxide contained in exhaust gas that effectively reduces the nitrogen oxide in the exhaust gas.

(b) Description of the Related Art

Generally, exhaust gas flowing out through an exhaust manifold from an engine is driven into a catalytic converter mounted at an exhaust pipe and is purified therein. After that, the noise of the exhaust gas is decreased while passing through a muffler and then the exhaust gas is emitted into the air through a tail pipe. The catalytic converter is a type of diesel particulate filter (DPF) and purifies pollutants contained in the exhaust gas. A catalytic carrier for trapping particulate material (PM) contained in the exhaust gas is in the catalytic converter, and the exhaust gas flowing out from the engine is purified through a chemical reaction.

One type of catalytic converter is a selective catalytic reduction (SCR) apparatus. In the selective catalytic reduction (SCR) apparatus, reductants such as carbon monoxide and total hydrocarbon (THC) react better with nitrogen oxide than oxygen. Thus, such a catalytic converter is called a selective catalytic reduction apparatus.

According to a conventional apparatus for reducing nitrogen oxide contained in exhaust gas, a diesel oxidation catalyst (DOC) device oxidizes total hydrocarbon (THC) and carbon monoxide (CO), and oxidizes nitrogen monoxide (NO) into nitrogen dioxide (NO₂). After that, an SCR device reduces nitrogen oxide (NO_(x)) into nitrogen gas (N₂) by using the NO₂ generated in the DOC device and a reductant. However, as exhaust gas regeneration (EGR) technology and post injection technology becomes applied to vehicles, the THC and the CO contained in an exhaust gas further increases. In addition, the NO₂ generated by oxidizing NO is used in the DOC device when the THC and the CO are oxidized in a cool starting. That is, the NO₂ is used when the THC and the CO are oxidized at low temperature.

In addition, if the NO₂ is generated in the DOC device, the NO₂ is used for regenerating soot in a catalyzed particulate filter (CPF) device disposed at the rear of the DOC device. Equation 1 below represents a soot regeneration reaction performed in the CPF device.

C+NO₂→CO/CO₂+NO  [Equation 1]

Therefore, it is difficult to reduce the NO_(x) by using the NO₂ generated in the DOC device according to the conventional apparatus for reducing nitrogen oxide contained in exhaust gas.

In addition, since, by applying the EGR technology and the post injection technology to the vehicles, the increased THC and CO are oxidized only in the DOC device, the THC and the CO are not fully oxidized.

The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.

SUMMARY OF THE INVENTION

Embodiments of the present invention has been made in an effort to provide an apparatus for reducing nitrogen oxide contained in exhaust gas having advantages of fully oxidizing THC and CO contained in the exhaust gas and sufficiently reducing NO_(x) as a consequence that a SCR device uses NO₂ generated when the THC and CO are oxidized.

An apparatus for reducing nitrogen oxide contained in exhaust gas according to an exemplary embodiment of the present invention may include: a diesel oxidation catalyst (DOC) device primarily oxidizing an exhaust materials containing total hydrocarbon (THC) and carbon monoxide (CO) in the exhaust gas by using a first diesel oxidation catalyst (DOC); a catalyzed particulate filter (CPF) device mounted downstream of the DOC device so as to receive the exhaust gas that is primarily oxidized by the DOC device, further oxidizing the exhaust materials containing the THC and the CO by heat generated during the primary oxidation and an oxidizing agent coated therein, and oxidizing nitrogen monoxide (NO) in the exhaust gas into nitrogen dioxide (NO₂) by using the generated heat and the oxidizing agent coated therein; a nozzle mounted downstream of the CPF device, and dosing a reductant to the exhaust gas; and a selective catalytic reduction (SCR) device mounted downstream of the nozzle, and reducing nitrogen oxide (NO_(x)) in the exhaust gas into nitrogen gas (N₂) by using the NO₂ generated in the CPF device and the reductant. The DOC device, the CPF device, the nozzle and the SCR device may be mounted on an exhaust pipe. The DOC device and the CPF device may be positioned upstream of the exhaust pipe and the nozzle and the SCR device may be mounted downstream of the exhaust pipe.

In another exemplary embodiment of the present invention, an apparatus for reducing nitrogen oxide contained in exhaust gas may further comprise a turbo charger mounted upstream of the DOC device, wherein the turbo charger is disposed apart from the DOC device by a predetermined distance such that the first oxidation reaction occurs at a good pace in the DOC device. The predetermined distance may be between about 100 mm and about 150 mm. The turbo charger, the DOC device, the CPF device, the nozzle and the SCR device may be mounted on an exhaust pipe. The turbo charger, the DOC device, the CPF device may be positioned upstream of the exhaust pipe and the nozzle and the SCR device may be mounted downstream of the exhaust pipe.

In further another exemplary embodiment of the present invention, a noble metal comprising platinum (Pt) and palladium (Pd) may be used for the first DOC in the DOC device, and a ratio of the platinum to the palladium may be 1:1-12:1. The diameter of the first DOC may be between about 100 mm and about 144 mm, and the length thereof is between about 100 mm and about 120 mm. A loading amount of the noble metal in the first DOC may be about 80-150 g/ft³.

In another exemplary embodiment of the present invention, the oxidizing agent may be coated at a catalyzed particulate filter (CPF) of the CPF device. A noble metal comprising Pt and Pd may be used for the oxidizing agent, and wherein a ratio of the Pt to the Pd is 2:1-6:1. A loading amount of the noble metal in the oxidizing agent may be 30-80 g/ft³. 60-80% of the oxidizing agent may be coated at a front portion in the CPF.

The reductant may be ammonia. The reductant may be dosed in form of urea.

The selective catalytic reduction (SCR) device may include a Fe-zeolite catalyst.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an apparatus for reducing nitrogen oxide contained in exhaust gas according to an exemplary embodiment of the present invention.

FIG. 2 is a flowchart showing processes performed by an apparatus for reducing nitrogen oxide contained in exhaust gas according to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

An exemplary embodiment of the present invention will hereinafter be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic diagram of an apparatus for reducing nitrogen oxide contained in exhaust gas according to an exemplary embodiment of the present invention.

As shown in FIG. 1, exhaust gas generated in an engine 10 flows sequentially through a turbo charger 20, a DOC device 30, a CPF device 40, a nozzle 50, and an SCR device 60, and noxious materials contained in the exhaust gas are removed. The turbo charger 20, the DOC device 30, the CPF device 40, the nozzle 50, and the SCR device 60 are mounted on an exhaust pipe 70.

The engine 10 includes a plurality of cylinders (not shown) for burning an air-fuel mixture. Each cylinder is connected to an intake manifold (not shown) so as to receive the air-fuel mixture, and the intake manifold is connected to an intake pipe (not shown) so as to receive fresh air.

In addition, each cylinder is connected to an exhaust manifold (not shown) and the exhaust gas generated in a combustion process is gathered in the exhaust manifold. The exhaust manifold is connected to the exhaust pipe 70.

The turbo charger 20 rotates a turbine (not shown) by using energy of the exhaust gas and an increases air drawing amount.

The DOC device 30 is mounted downstream of the turbo charger 20, and is disposed apart from the turbo charger 20 by a predetermined distance L1 such that a first oxidation occurs at a good pace in the DOC device 30. The predetermined distance L1 may be 100-150 mm.

A first DOC is coated in the DOC device 30, and a noble metal including platinum (Pt) and palladium (Pd) is used for the first DOC. In order to effectively perform the first oxidation, the ratio of the platinum to the palladium may be 1:1-12:1 and the loading amount of the noble metal may be 80-150 g/ft³. In addition, the flow of the exhaust gas must have a constant diameter in order to perform the first oxidation. For this purpose, the diameter of the first DOC may be 100-144 mm, and the length thereof may be 100-120 mm.

The DOC device 30 oxidizes an exhaust materials containing THC and CO in the exhaust gas primarily, and transmits the oxidized exhaust gas to the CPF device 40 mounted downstream thereof. In addition, the DOC device 30 transmits heat generated during the primary oxidation of the exhaust materials containing the THC and the CO to the CPF device 40 such that the heat is used in a secondary oxidation. The primary oxidation performed in the DOC device 30 is described in the following Equation 2.

4HC+3O₂→2CO₂+2H₂O

2CO+O₂→2CO₂  [Equation 2]

The CPF device 40 is mounted downstream of the DOC device 30 and receives the exhaust gas primarily oxidized in the DOC device 30 and the heat generated in the primary oxidation. The CPF device 40 is provided with a CPF mounted therein and filters PM contained in the exhaust gas. In addition, a second DOC (that is, an oxidizing agent) is coated in the CPF such that the exhaust materials containing the THC and the CO are secondarily oxidized therein and NO is oxidized into NO₂. Since the secondary oxidation of the exhaust materials containing the THC and the CO in the CPF device 40 is performed by using the heat of the DOC device 30, NO₂ is not used in the secondary oxidation. Therefore, NO₂ is generated in the CPF device 40.

In order to effectively use the heat of the DOC device 30, 60-80% of the second DOC is coated at a front portion in the CPF. A noble metal including the platinum (Pt) and the palladium (Pd) is used for the second DOC. In order to prevent the reducing ratio of the NO_(x) from being deteriorated because of excess generation of the NO₂, the ratio of the platinum to the palladium in the second DOC may be 2:1-6:1, and the loading amount of the noble metal may be 30-80 g/ft³.

The secondary oxidation performed in the CPF device 40 is described in the following Equation 3.

4HC+3O₂→2CO₂+2H₂O

2CO+O₂→2CO₂

2NO+O₂2NO₂  [Equation 3]

The nozzle 50 is mounted downstream of the CPF device 40, and doses a reductant to the exhaust gas secondarily oxidized in the CPF device 40. The reductant may be ammonia. Generally, urea is dosed into the exhaust gas by the nozzle 50 and the urea is decomposed into ammonia.

The exhaust gas mixed with the reductant and the NO₂ generated in the CPF device 40 are transmitted to the SCR device 60.

The SCR device 60 is mounted downstream of the nozzle 50, and includes a Fe-zeolite catalyst. The SCR device 60 reduces NO_(x) contained in the exhaust gas into nitrogen gas (N₂) by using the NO₂ generated in the CPF device 40 and the reductant dosed through the nozzle 50 so as to reduce the NO_(x) amount in the exhaust gas.

The reaction performed in the SCR device 60 is described Equation 4 below.

4NH₃+4NO+O₂→4N₂+6H₂O

2NH₃+NO+NO₂→2N₂+3H₂O

8NH₃+6NO₂→7N₂+12H₂O  [Equation 4]

Hereinafter, operations of the apparatus for reducing nitrogen oxide contained in exhaust gas according to an exemplary embodiment of the present invention will be described in detail.

FIG. 2 is a flowchart showing processes performed by an apparatus for reducing nitrogen oxide contained in exhaust gas according to an exemplary embodiment of the present invention.

As shown in FIG. 2, the exhaust gas burned in the engine 10 and passing through the turbo charger 20 flows into the DOC device 30, and the DOC device 30 primarily oxidizes the exhaust materials containing the THC and the CO in the exhaust gas at a step S110.

The primarily oxidized exhaust gas and the heat generated in the primary oxidation are transmitted to the CPF device 40, and the CPF device 40 secondarily oxidizes the exhaust materials containing the THC and the CO in the exhaust gas at a step S120. In addition, the CPF device 40 oxidizes the NO in the exhaust gas into the NO₂ at a step S130.

After that, the nozzle 50 doses the reductant at a step S140 into the exhaust gas that is secondarily oxidized, and the exhaust gas is transmitted to the SCR device 60.

The SCR device 60 reduces the NO_(x) into the N₂ at a step S150 by using the NO₂ generated in the CPF device 40 and the reductant dosed by the nozzle 50.

According to the present invention, since THC and CO are primarily oxidized in a DOC device and are secondarily oxidized in a CPF device by using heat generated in the primary oxidation, amount of the THC and the CO contained in exhaust gas may be sufficiently reduced.

In addition, since NO is oxidized into NO₂ by using heat generated when the THC and the CO are oxidized in the DOC device and an SCR device reduces NO_(x) by using the NO₂, the amount of the NO_(x) contained in the exhaust gas may be sufficiently reduced.

While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 

1. An apparatus for reducing nitrogen oxide contained in exhaust gas, comprising: a diesel oxidation catalyst (DOC) device primarily oxidizing an exhaust materials containing total hydrocarbon (THC) and carbon monoxide (CO) in the exhaust gas by using a first diesel oxidation catalyst (DOC); a catalyzed particulate filter (CPF) device mounted downstream of the DOC device so as to receive the exhaust gas that is primarily oxidized by the DOC device, further oxidizing the exhaust materials containing the THC and the CO by heat generated during the primary oxidation and an oxidizing agent coated therein, and oxidizing nitrogen monoxide (NO) in the exhaust gas into nitrogen dioxide (NO₂) by using the generated heat and the oxidizing agent coated therein; a nozzle mounted downstream of the CPF device, and dosing a reductant to the exhaust gas; and a selective catalytic reduction (SCR) device mounted downstream of the nozzle, and reducing nitrogen oxide (NO_(x)) in the exhaust gas into nitrogen gas (N₂) by using the NO₂ generated in the CPF device and the reductant.
 2. The apparatus of claim 1, wherein the DOC device, the CPF device, the nozzle and the SCR device are mounted on an exhaust pipe.
 3. The apparatus of claim 3, wherein the DOC device and the CPF device are positioned upstream of the exhaust pipe and the nozzle and the SCR device are mounted downstream of the exhaust pipe.
 4. The apparatus of claim 1, further comprising a turbo charger mounted upstream of the DOC device, wherein the turbo charger is disposed apart from the DOC device by a predetermined distance such that the first oxidation reaction occurs at a good pace in the DOC device.
 5. The apparatus of claim 4, wherein the predetermined distance is between about 100 mm and about 150 mm.
 6. The apparatus of claim 5, wherein the turbo charger, the DOC device, the CPF device, the nozzle and the SCR device are mounted on an exhaust pipe.
 7. The apparatus of claim 6, wherein the turbo charger, the DOC device, the CPF device are positioned upstream of the exhaust pipe and the nozzle and the SCR device are mounted downstream of the exhaust pipe.
 8. The apparatus of claim 1, wherein a noble metal comprising platinum (Pt) and palladium (Pd) is used for the first DOC in the DOC device, and wherein a ratio of the platinum to the palladium is 1:1-12:1.
 9. The apparatus of claim 8, wherein the diameter of the first DOC is between about 100 mm and about 144 mm, and the length thereof is between about 100 mm and about 120 mm.
 10. The apparatus of claim 9, wherein a loading amount of the noble metal in the first DOC is about 80-150 g/ft³.
 11. The apparatus of claim 1, wherein the oxidizing agent is coated at a catalyzed particulate filter (CPF) of the CPF device.
 12. The apparatus of claim 11, wherein a noble metal comprising Pt and Pd is used for the oxidizing agent, and wherein a ratio of the Pt to the Pd is 2:1-6:1.
 13. The apparatus of claim 12, wherein a loading amount of the noble metal in the oxidizing agent is 30-80 g/ft³.
 14. The apparatus of claim 13, wherein 60-80% of the oxidizing agent is coated at a front portion in the CPF.
 15. The apparatus of claim 1, wherein the reductant is ammonia.
 16. The apparatus of claim 15, wherein the reductant is dosed in form of urea.
 17. The apparatus of claim 1, wherein the selective catalytic reduction (SCR) device includes a Fe-zeolite catalyst. 